The Principle of the Vacuum Circuit Breaker in the High-voltage Switchgear
The **vacuum circuit breaker** in the high-voltage switchgear is a kind of switching equipment that uses the **high-vacuum environment** to extinguish the arc, and it is widely used in the protection and control of the power system. The following are its core principles, structures, and application key points:
1. Core Working Principles
Arc Extinguishing Mechanism
- **Vacuum Environment**: The inside of the arc extinguishing chamber is a high vacuum of **less than 10⁻⁴ Pa**. An arc cannot continuously burn in a vacuum (there is no gas ionization medium).
- **Contact Separation**: When the circuit breaker trips, the moving and static contacts separate quickly. The generated arc is rapidly extinguished because it cannot be maintained in the vacuum environment.
- **Metal Shield**: It absorbs the energy of the arc and prevents the insulation from decreasing due to the evaporation of the contact material.
Operation Process
1. **Closing**: The operating mechanism drives the contacts to close, establishing a conductive path.
2. **Tripping**: When a fault occurs, the protection device triggers the tripping mechanism, the contacts separate quickly, and the arc is extinguished in the vacuum environment.
2. Key Structural Components
- **Vacuum Arc Extinguishing Chamber**: The core component, which includes moving/static contacts, a shield, and a bellows (to achieve mechanical movement).
- **Operating Mechanism**: An electric or manual energy storage mechanism (such as a spring energy storage mechanism) that provides the power for closing and tripping.
- **Control Unit**: It interacts with the relay protection device and receives the closing and tripping signals.
- **Insulating Supports**: Epoxy resin or ceramics are used to support the arc extinguishing chamber and isolate the high voltage.
3. Main Characteristics
Advantages
- **Strong Arc Extinguishing Ability**: The arc is quickly extinguished in a vacuum, and the breaking capacity can reach **12.5 to 63 kA**.
- **Low Maintenance Cost**: There is no oil and no SF6 gas, and there is no need to replace the medium regularly.
- **Long Life**: The mechanical life can reach more than **10,000 times**, and the electrical life is limited by the contact material.
- **Small Size**: The structure is compact, suitable for the miniaturization design of high-voltage switchgear.
Limitations
- **Voltage Level Limitation**: It is mostly used in **12 to 40.5 kV** systems. For higher voltages, arc extinguishing chambers need to be connected in series.
- **Overvoltage Risk**: When breaking an inductive load, a chopping overvoltage may occur, and it needs to be used in conjunction with a lightning arrester.
4. Typical Application Scenarios
- **Power System**: Line protection for substations and switchgear with a voltage of 35 kV and below.
- **Industrial Field**: Control and protection of equipment such as motors and transformers.
- **New Energy**: Fast switches for wind power and photovoltaic grid-connected systems.
5. Safety and Maintenance
- **Vacuum Degree Detection**: Regularly use a **vacuum degree tester** to check the airtightness of the arc extinguishing chamber (a decrease in the vacuum degree will lead to the failure of arc extinguishing).
- **Contact Wear Monitoring**: Determine whether it is necessary to replace the contacts according to the number of breaking times or the contact travel.
- **Lubrication of the Operating Mechanism**: Ensure that components such as the energy storage spring and the connecting rod move flexibly.
6. Comparison with Other Circuit Breakers
| Type | Arc Extinguishing Medium | Breaking Capacity | Maintenance Requirement | Environmental Friendliness |
| Vacuum Circuit Breaker | Vacuum | High | Low | No Pollutants |
| SF6 Circuit Breaker | SF6 Gas | Extremely High | Medium | SF6 Greenhouse Effect |
| Minimum Oil Circuit Breaker | Insulating Oil | Low | High | Risk of Oil Pollution |
7. Fault Cases and Prevention
- **Contact Welding**: Overload during closing or oxidation of the contacts leads to welding. The contact surface needs to be cleaned regularly.
- **Bellows Rupture**: Mechanical fatigue or external force damage leads to the loss of vacuum degree, and the arc extinguishing chamber needs to be replaced.
- **Control Circuit Fault**: The closing and tripping coils are burned out. The insulation of the secondary circuit and the voltage stability need to be checked.
If you need to further understand the selection criteria (such as breaking capacity, operating voltage) or installation specifications (such as GB 1984-2014), specific parameters can be provided to assist in the analysis!
